1. Field of the Invention
The present invention relates to a method of detection of an abnormality of a squeeze pin and a molding machine such as die cast machine having a squeeze pin.
2. Description of the Related Art
A molding machine such as die cast machine can use a squeeze pin to apply pressure to the material being molded. The squeeze pin prevents gross porosity. Such a system is disclosed in Japanese Patent Publication (A) No. 9-225619. In such a molding machine, in order to make the squeeze pin advance toward the cavity with a proper stroke, even where galling of the squeeze pin has occurred, for example, the oil pressure or flow in a hydraulic cylinder for driving the squeeze pin has been raised or the time that the squeeze pin begins to advance in the next cycle is made earlier when the galling of the squeeze pin has occurred.
The above technology controls the operation of the squeeze pin based on various types of measurement values obtained while the squeeze pin advances in the cavity filled with molten material. In other words, galling of the squeeze pin is detected while molten material is around the squeeze pin. However, a change in the environment, such as a change in the mold temperature or oil temperature, will cause the flow and solidification state of the molten material in the cavity to differ for each shot (for each cycle). Accordingly, in the conventional detection of galling of a squeeze pin, variations arise in the operation of the squeeze pin among cycles due to the influence of the flow and solidification state of the melt around the squeeze pin, so galling of the squeeze pin cannot be stably detected. For this reason, if, for example, the occurrence of galling is accidentally detected in a cycle due to the influence of the flow etc. in the cavity, and if the time that the squeeze pin begins to advance in the next cycle is set early, an excessively large stroke of the squeeze pin will occur in the next cycle.